Visualization of Somatostatin Receptors and Correlation with Immunoreactive Growth Hormone and Prolactin in Human Pituitary Adenomas: Evidence for Different Tumor Subclasses

Abstract

Using combined autoradiographic and immunohistochemical techniques, specific somatostatin (SRIH) receptors were measured in 31 human pituitary tumors. SRIH receptor distribution was compared with that of immunoreactive GH and PRL in the same tissue sections. Among the 10 tumors from acromegalic patients, 7 contained a high or medium density of SRIH receptors, whereas only a low density of such receptors was present in the remaining 3 tumors despite a comparably high concentration of immunoreactive GH in all 10 tumors. No correlation between plasma GH levels and SRIH receptors was found. One corticotroph tumor was SRIH receptor negative. Among the 5 prolactinomas tested, only 1 contained a significant density of SRIH receptors, the distribution of which did not correlate with that of immunoreactive PRL cells. Interestingly, among the 15 endocrine-inactive adenomas investigated, 6 had a measurable, sometimes high, density of SRIH receptors despite undetectable GH, PRL, or TSH immunoreactivity. These results suggest that based on their SRIH receptor content, there may be subclasses of GH-producing pituitary adenomas. The difference in SRIH receptor density may be an explanation for the clinically described differential responsiveness of acromegalic patients to SRIH. The results also suggest that subclasses of endocrine-inactive pituitary adenomas may exist; some of them contain significant amounts of SRIH receptors, which may be responsive to SRIH treatment.